Hello,
I've got a Luxman LV-105U with a faulty balance pot (alps 254MN 250k dual).
One of the two gangs has a resistance of 250k but the other is at 300k which is causing quite a difference in output between both channels. I tried cleaning, checked for cracks but I don't think there's anything more I can do to save it.
An exact replacement seems impossible to find (or maybe I didn't look in the right places) so I'm looking for something similar. I know ALPS are still making pots that look like this one but 250k versions don't seem to exist any more.
I've got a Luxman LV-105U with a faulty balance pot (alps 254MN 250k dual).
One of the two gangs has a resistance of 250k but the other is at 300k which is causing quite a difference in output between both channels. I tried cleaning, checked for cracks but I don't think there's anything more I can do to save it.
An exact replacement seems impossible to find (or maybe I didn't look in the right places) so I'm looking for something similar. I know ALPS are still making pots that look like this one but 250k versions don't seem to exist any more.
The thing is when I got it, there was no sound at all on the channel that now is weaker that the other. cleaning the pot took car of that but the amount of difference between left and right seems to get worse again, I cleaned it again and it got better but I can imagine it won't stay this way very long.
Can you use something like this and just adapt it to the PCB:
PDB182-GTRB1-254MN Bourns | Mouser Australia
50k additional resistance seems a lot. What did you try to clean it with?
PDB182-GTRB1-254MN Bourns | Mouser Australia
50k additional resistance seems a lot. What did you try to clean it with?
I don't really need to keep the pcb, I can connect the wires directly so that's not a problem. adapting the knurled shaft to the knobs that are made for a flatted d shaft will maybe be a little harder, I don't think they have these.
I cleaned it with a European equivalent of deoxit. I even opened it and cleaned it several times with a soft toothbrush and some paper towel with the product. I use this a lot and it worked well so far. I think this one is really just too far gone.
I cleaned it with a European equivalent of deoxit. I even opened it and cleaned it several times with a soft toothbrush and some paper towel with the product. I use this a lot and it worked well so far. I think this one is really just too far gone.
I was going to suggest DeOxit as it is pretty good for getting the oxidation off.
Sometimes considering the time to repeatedly fix versus replacing with a new item, it is better to just put something reliable in and have done with it. (Unless there are sensitivities about keeping it original).
They do smooth shafts as well, which may be easier to file a flat into:
PDB182-GTRB2-254MN Bourns | Mouser Australia
Sometimes considering the time to repeatedly fix versus replacing with a new item, it is better to just put something reliable in and have done with it. (Unless there are sensitivities about keeping it original).
They do smooth shafts as well, which may be easier to file a flat into:
PDB182-GTRB2-254MN Bourns | Mouser Australia
That's exactly why I would prefer to replace it.
Isn't this a simple volume pot ? Wouldn't a balance pot need to have two parts on each gang, a resistive part up until the centre point and next a conductive part and the opposite on the other gang so that when the pot is in the middle both channel have no resistance at all ?
Could I use a single ganged pot of 500k (linear), connect each channel to one side and the wiper to ground or would that mess with the channel separation ?
Like this one : RV120F-10-15F-B500K-0075 Alpha (Taiwan) | Mouser France
Isn't this a simple volume pot ? Wouldn't a balance pot need to have two parts on each gang, a resistive part up until the centre point and next a conductive part and the opposite on the other gang so that when the pot is in the middle both channel have no resistance at all ?
Could I use a single ganged pot of 500k (linear), connect each channel to one side and the wiper to ground or would that mess with the channel separation ?
Like this one : RV120F-10-15F-B500K-0075 Alpha (Taiwan) | Mouser France
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Depends on how the circuit is set up, it could be center detent or plain pot.
The balance control is on the bottom middle of the attached schematic. It appears to be a standard dual gang pot set up so that as the resistance increases to one channel, the inverse is applied to the other.
It's late here so have a good look for yourself (or investigate your pots with a DMM to see how they behave) and decide which type is right for you.
The balance control is on the bottom middle of the attached schematic. It appears to be a standard dual gang pot set up so that as the resistance increases to one channel, the inverse is applied to the other.
It's late here so have a good look for yourself (or investigate your pots with a DMM to see how they behave) and decide which type is right for you.
Attachments
How To - Car Stereo - Nine Ways to Adjust Signal Level
Balance control, figure 4 is how I imagine this is set up.
Balance control, figure 4 is how I imagine this is set up.
From what I see inside the pot and my measurements it is how I described before, one channel has a carbon track on the right side to ground and the other has a carbon track on the left side to ground. The rest of the track is just metal and goes to both inputs. The wipers are the output. When the pot is in the middle (where it locks) the wipers for both channels are just at the limit between metal track and carbon track (so 250k to ground. When I turn the pot left, the wiper for the right channel moves on the carbon track and finally gets shorted to ground, same the other way. The schematic illustrates this perfectly btw.
If I use a simple stereo 250k pot, when set in the middle it will measure 125k between wiper and input and wiper to output.
If I use a simple stereo 250k pot, when set in the middle it will measure 125k between wiper and input and wiper to output.
My Vestax MDM401 mixer uses the same principle. What I did was removing the balance pot and shunting it for a quick fix .. Now have to find something similar.
I believe it behaves as there were one pot for each channel. That means when You attenuate one channel, the other doesn't increase level. The channels are indeed separated. On my Vintage Pioneer SA606 it is single ganged. I would try both and see how they behave.
I believe it behaves as there were one pot for each channel. That means when You attenuate one channel, the other doesn't increase level. The channels are indeed separated. On my Vintage Pioneer SA606 it is single ganged. I would try both and see how they behave.
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